THE  MEASUREMENT  OF  THE  MIND         223
level of humanity. But this doctrine is somewhat discredited
nowadays, for we all possess to some extent these marks of
degeneracy.
In fact, as Dr Cyril Burt says, "Psychologists are nowadays
agreed in distrusting all snapshot judgments based upon an
inspection of the face and head." x Such methods of in-
vestigation have not yet recovered from the researches On the
Relationship of Intelligence to Size and Shape of the Head, published
by Professor Karl Pearson in 1906. This investigator, from
an examination of 5000 school children and 1000 under-
graduates, concluded that no reliance was to be placed on
such vicarious measurements of the mind — that no prediction
of intellectual qualities could be made from physical features.
"We cannot tell a criminal by looking at him; we cannot tell
a genius by the shape of his skull ; and we cannot tell a fool
by the length of his ears." a Pearson reached his conclusion
by means of mathematics, devising, along with Galton, a
powerful mathematical method for drawing indubitable con-
clusions from masses of data. There is no space here to enter
into it fully, but the general idea may perhaps be conveyed by
the following example.
Suppose a number of people, whom we shall call A, B, Cs
. . . X, Y, £, are tested for immediate memory, and an order
of merit drawn up, A being first with mark a, B second with
mark b, . . . T second last with markj>3 and £last with mark
£. Suppose further that the same people are tested for pro-
longed memory and again a list drawn up in order of scores.
It might conceivably happen that the order and the marks for
the second test would be exactly the same as for the first, A, 2?,
C, . . . -5T, T,£ having marks a, b,c, . . . x, j>, z in both tests.
In **"« case we should have what is called perfect positive
correlation between the two tests, meaning that from a person's
score in the one we can infer exactly what his score will be in
the other, or that the two functions tested are the same. It
might also happen that the second list would turn out to be the
first one reversed, ,£ having mark a, T mark b, . .
1 Psychological Tests ofEducable Capacity (Board of Education), p. 4.
* Ballard, Mental Tests, pp. 6, 7.